rust-status: refactor dispatch case for normal files
This should make the code easier to read and more idiomatic.
Differential Revision: https://phab.mercurial-scm.org/D7300
rust-status: return a ParallelIterator instead of a Vec from stat_dmap_entries
This allows the caller function to choose when and how the iteration and/or
collection happens. This change also cleans up the now unused `filter_map`.
Differential Revision: https://phab.mercurial-scm.org/D7299